Re: check if memory is accessible

On Dec 27, 12:06 pm, rakesh uv <uvrak...@xxxxxxxxx> wrote:
On Dec 27, 5:14 am, phil-news-nos...@xxxxxxxx wrote:





On Wed, 26 Dec 2007 02:11:08 -0800 (PST) rakesh uv <uvrak...@xxxxxxxxx> wrote:
| On Dec 24, 11:08 pm, Mike <michael.h.william...@xxxxxxxxx> wrote:
|> On Dec 24, 4:23 am, rakesh uv <uvrak...@xxxxxxxxx> wrote:
|>
|> > Hi,
|> >       Does there exist an assembly instruction to check if a
|> > particular memory is accessible
|>
|> > Best Regards,
|> > Rakesh UV
|>
|> I do not understand the question. Can you re-phrase it?
|>
|> -Mike
|
| since every process has its own address space and it would be killed
| if it tries to access some one else or read only address space.
| i was thinking of a method which would help me in finding that whether
| an address is accessible or not before actually reading /writing

If it is a method, rather than a CPU instruction, you seek, then open and
read the file "/proc/self/maps" and see if the address of interest is in
that list or not.

--
|---------------------------------------/----------------------------------­|
| Phil Howard KA9WGN (ka9wgn.ham.org)  /  Do not send to the address below |
| first name lower case at ipal.net   /  spamtrap-2007-12-26-1...@xxxxxxxx |
|------------------------------------/-------------------------------------­|

i know a method named access_ok defined in asm/uaccess.h which is used
by kernel modules
and there exist a assembly instruction named PROBER in VAX.
i would like to give an simple example
stringcopy(str1 , str2)
suppose str1 or str2 are result of  some functions,not in my control
and if before passing it to stringcopy if i am able check the
validity of address, i would be able to provide some alternative str1
and str2(some valid strings).

i was debugging my application with gdb (it was getting a segmention
fault ) , since i was using GDB, i was able to control the flow and i
was able to know that the address was invalid, prior to calling
stringcopy, just by using the command
print str1
gdb informed me that the address is not accessible.

I wished that if i was able to find it by myself as done by
gdb............. and this triggered me to put this question!!

Thank you
Rakesh UV- Hide quoted text -

- Show quoted text -

An invalid address? Does GDB show that the address contained in str1
is NULL or something? Or do you have an actual address which in turn
contains garbage?
I dont think there's any address which is not accessible unless it
points to NULL in which case, a "print str1" statement would thow an
exception. Please clarify.
.

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